The present invention relates to a gear-change system for bicycles, of the type comprising:
a (front or rear) derailleur for controlling selective engagement of a bicycle chain on a plurality of gear wheels (sprockets or crank gears);
a device for controlling the derailleur;
a flexible control cable which connects the control device to the derailleur;
an electronic display for displaying the operating condition of the gear-change system; and
a sensor for detecting the operating position of said control device, designed to emit at output a signal indicating the said position and to send the signal to the said electronic display, the said sensor being associated to said flexible cable and comprising:
a shell which is traversed by said flexible cable;
a movable reference member which moves together with the cable inside the shell; and
sensing means for detecting the position of said reference member with respect to the shell.
A gear-change system of the type specified above, which uses in particular a sensor for detecting the position of the flexible control cable of the aforesaid type, is described and illustrated in EP-A-0 820 926 and in the corresponding document U.S. Pat. No. 5,903,214. In the case of the said known solution, the above-mentioned sensing means for detecting the position of the movable reference member are sensing means without contact, typically a magnetic sensor.
Also known in the prior art are sensors for detecting the operating condition of the gearing system which are not associated to the flexible control cable but rather are mounted directly on the gear-change control device.
Finally, also known in the prior art are sensor-display means for detecting and displaying the operating condition of the bicycle gearing system which consist simply of a reference member associated to the flexible control cable and co-operating with a reference scale present on the shell within which the reference member moves (see, for instance, DE-U-91 13 406 and EP-A-0 647 556). This latter solution uses the device described above both as a sensor device and directly as a display device, and consequently is not suited for more sophisticated applications which make use of a display of an electronic type.
The purpose of the present invention is to provide a system of the type indicated at the beginning of the present description, i.e., one which is suitable for detecting the operating condition of the gearing system and can be associated to an electronic display, is simple from the constructional standpoint, is reliable, and has a relatively low cost.
With a view to achieving the above purpose, the subject of the invention is a system of the type indicated at the beginning of the present description, characterized in that the aforesaid detecting means consist of a potentiometric sensor comprising a movable contact carried by said reference member, and at least one electrically conductive channel mounted inside the shell of the sensor, on which said movable contact is fitted in such a way that it can slide.
Consequently, in the system according to the invention the sensor device for detecting the operating condition of the gearing is associated to the flexible control cable at any point intermediate between the control device and the derailleur controlled thereby. Consequently, from this standpoint the device according to the invention is of the same type as the device which forms the subject of the document EP-A-0 820 926 and distinguishes itself instead from the other solutions that enable display of the operating condition of the gearing system on an electronic display by making use of a sensor associated directly to the gear-change control device. At the same time, the device is simpler and more reliable than the devices of the prior art described above in so far as it makes use of a potentiometric sensor have the simplified structure described previously.
Of course, the present invention refers both to the gearing system that uses the aforesaid sensor device and to the aforesaid sensor device considered in itself.